Table 25: Abortion and breast cancer risk

This summary table contains detailed information about research studies. Summary tables are a useful way to look at the science behind many breast cancer guidelines and recommendations. However, to get the most out of the tables, it’s important to understand some key concepts. Learn how to read a research table.

Introduction: Research clearly shows abortion (also called induced abortion) does not increase the risk of breast cancer.

Since 2003, the American College of Obstetricians and Gynecologists (ACOG) and the National Cancer Institute (NCI) and have agreed the scientific evidence does not support a link between abortion and breast cancer [1-2].

The ACOG and the NCI routinely review the evidence on this topic and continue to agree there’s no link between abortion and breast cancer [1-2]. ACOG reaffirmed their conclusion that there is no link between abortion and breast cancer in 2018.

The importance of study design for research on abortion and breast cancer risk

Some case-control studies have suggested abortion may increase the risk of breast cancer. However, the design of case-control studies makes the accuracy of these results questionable.

Case-control studies rely on the reporting of past behavior. When it comes to a sensitive subject like abortion, this can have a big impact on the information gathered.

The cases in these studies (the women with breast cancer) may be much more likely to give complete information about their abortion history than the controls (the women without breast cancer). Such differences in reporting bias study results.

Prospective cohort studies are much more likely to give accurate results on topics such as abortion. These studies gather sensitive information before women are diagnosed with breast cancer. This helps limit biased reporting.

The large cohort studies below show abortion does not increase the risk of breast cancer.

Miscarriage and breast cancer risk

Further supporting the evidence that abortion does not increase breast cancer risk are findings from studies on miscarriage (also called spontaneous abortion) and the risk of breast cancer. Findings from cohort studies, a meta-analysis and a large pooled analysis show miscarriage does not increase the risk of breast cancer [3-10].

Since 2003, the NCI has concluded miscarriage is not linked to breast cancer [1]. The NCI routinely reviews the evidence on this topic (most recently in 2016) and continues to agree the evidence does not support a link between the two [1].